1. Field of the Invention
The present invention relates to a ball bearing slide unit for linear motion wherein said slide unit is mounted on a track rail of rectangular cross section which is provided with linear track surfaces symmetrically at both vertical side surfaces, and is provided with track surfaces opposing said track surfaces on said track rail, with linear return holes running parallel to said track surfaces, and with direction changing paths which connect the both ends of said track surfaces and said return holes respectively, and is further formed with circulating paths where a group of balls endlessly circulate supporting a load and rolling between opposing track surfaces. The present invention particularly relates to the circulating path in which the group of balls, which supports said slide unit endlessly circulates.
2. Description of the Prior Art
In the prior art ball bearing structure for linear motion, as shown in FIG. 16 and FIG. 17, the mounting surface 50, on which the slide unit 49 mounts on the track rail 48, is an inclined surface. The group of balls 53 supporting the load between the track surface 51 of the track rail 48 and the track surface 52 of the slide unit 49 are always pressed against both track surfaces 51, 52 by the imposed load. Therefore, no preload against the track surface is necessary. However, side plate 56, in which direction changing path 55 is formed to circulate the balls 53 from the load zone formed by both track surfaces 51, 52 to the no load zone formed by return hole, is directly connected to the ends of said load zone formed by both track surfaces 51, 52 and to the ends of return holes, which are the linear paths of the slide unit 49, and said track surface 52 and return hole 54 are located in parallel and close together at position normal to the mounting surface 50. Therefore, as shown in FIG. 17, an abrupt direction change of the ball 53 is made at a small portion of length l. At this direction changing path 55, there will occur friction between the ball 53 and the circularly shaped outer wall surface of the direction changing path 55. A locking state will occur when the neighbouring balls 53 are pressed against said wall. Thus defects which prevent the smooth progression of the balls existed. In order to overcome these defects, it was necessary to increase the distance between the track surface 52 and the return hole 54 and to increase said distance l to make the curvature of direction changing path 55 small. This resulted in large size of the slide unit in the longitudinal and left and right directions, Also, if size was not increased, load zone had to be decreased. Since this results in the increase of load per unit length at the load zone, there was a defect that the load capacity of the slide unit 49 was decreased.
Also, the prior art side plate of the ball bearing slide unit for linear motion was usually made by casting and was heavy. Since the direction changing path provided has to be machined, it was difficult to make it into any complex curved surface, and machining and material costs were high. Besides, since its weight is large, when assembled, the total weight became high. Thus there was a limit in its use for assembly as part of the machine parts. Therefore, there was a demand of a side plate having a direction changing path with less defects such as described above.